Cardiac auscultation refers to the process of determining cardiac well-being or illness by listening to the heart through a stethoscope. The results obtained by means of these techniques can, however, be very subjective and depend to a large extent on the experience and acquired knowledge of the diagnosing health care worker.
The majority of cardiac abnormalities manifest themselves as cardiac murmurs. However, not all murmurs are pathological. Innocent heart murmurs are sounds made by blood circulating through heart chambers and valves or blood vessels near the heart. Innocent heart murmurs are more common in children and are considered to be harmless.
Echo-cardiography is a technique which is considered by many to be one of the, if not the, most accurate aids in the field. It utilises ultrasound technology to generate visual images of the beating heart, but requires advanced training, skill and experience to manipulate the ultrasound probe in order to obtain useful images. An echo-cardiography system will, however, require an investment of close to ZAR1 Million at the time of writing, excluding costs associated with, for example, the training of staff to operate the system and meaningfully analyze the images obtained. This high cost means that echo-cardiography systems are not a feasible option for the majority of healthcare institutions in less affluent areas.
It is estimated that up to 90% of paediatric patients will exhibit some form of heart murmur on examination, although less than 1% will eventually turn out to have a congenital heart defect. Although most paediatric cardiologists can diagnose an innocent heart murmur with a very high degree of accuracy, sensitivity and specificity, even a routine paediatric cardiology evaluation is generally too costly for people from middle to low income groups.
This is particularly true in the context of a large number of developing countries, such as South Africa, where, in addition to the high cost of paediatric cardiology evaluations, patients often have to travel long distances from rural communities in order to visit one of the few paediatric cardiologists available for the population of approximately 48 million people. The referral of paediatric patients to paediatric cardiologists can therefore become extremely difficult and in most cases impractical from a logistical point of view.
When a serious congenital cardiac defect goes undetected, the physical, socio-economical and emotional damage to the patient and his or her caretakers can be enormous.
It is therefore of the utmost importance that private healthcare physicians and nurses who look after paediatric patients must be able to determine which patients will require additional evaluation as well as the urgency with which such evaluation should be conducted.
The only assistance presently available to healthcare workers to evaluate heart sounds is the common stethoscope, which can be either mechanical or electronic. Besides the rate and frequency (pitch) of the heart sounds, morphological features, which might provide an important indication of a critical heart disorder, may be undetectable by the human ear.
A low cost, portable, digital system for analyzing heart sounds and making preliminary diagnoses would therefore be a very useful instrument to healthcare workers operating in the field. In order to be useful in such an automated system, recorded heart sounds must, however, be digitised and pre-processed for optimal feature extraction. Only once such pre-processing has been done will the signals be useful in a decision making network. Naturally, the more accurately features can be extracted, the more accurate the resulting diagnoses may be.
In the remainder of this specification the term “QRS complex” should be understood as a name for some of the deflections seen on a typical electrocardiogram (ECG) signal. It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the right and left ventricles. Classically the ECG tracing has 5 deflections, arbitrarily named P to T waves (in some conditions there is a U wave as well). The Q, R and S waves occur in rapid succession, do not all appear in all leads and reflect a single event so are thus normally considered as a whole complex. A Q-wave is any downward deflection after the P-wave. An R-wave is an upward deflection and the S wave is any downward deflection after the R-wave. In the remainder of this specification the term “QRS peaks(s)” should be interpreted as having a corresponding meaning.